The present invention relates to photoelectric sensing devices, and in particular to a photoelectric sensing device that provides for variable control of the hysteresis of a photoelectric sensor (xe2x80x9cphotosensorxe2x80x9d) contained within the device so as to allow for a reduction or increase in the hysteresis of the photoelectric sensor in accordance with the environment/application the photosensor is being utilized.
Substantially, every photosensor (also known as a photo IC) is designed such that upon receiving a predetermined amount of light, the output of the photosensor is toggled to a given state (e.g., logic high) so as to indicate that the photosensor has received an amount of light exceeding the predetermined level. This first predetermined level is referred to as the xe2x80x9clight statexe2x80x9d trip point or the xe2x80x9cdark-to-lightxe2x80x9d threshold. Then, as the amount of light received by the photosensor declines, there is a second predetermined level at which the output of the photosensor will toggle again so as to indicate that the amount of received light is below a second predetermined level. This second predetermined level is referred to as the xe2x80x9cdark statexe2x80x9d trip point or the xe2x80x9clight-to-darkxe2x80x9d threshold. The difference between the xe2x80x9clight statexe2x80x9d trip point and the xe2x80x9cdark statexe2x80x9d trip defines the hysteresis of the photosensor.
As is known, it is necessary for the photosensor to have hysteresis in order to prevent the photosensor""s output from inadvertently switching or xe2x80x9cchatteringxe2x80x9d due to, for example, electrical interference, minute changes in the level of light received by the photosensor, high frequency light, or pulsing EM fields, etc. However, it is also desirable to adjust the hysteresis of the photosensor in accordance with the application in which the photosensor is being utilized.
More specifically, in low contrast sensing environments, the photosensor needs to be able to resolve (i.e., detect) small changes in light. In order to accomplish this task, the hysteresis of the photosensor needs to be low. An example of a low contrast environment is a system for use with an automatic envelope stuffing machine, which is required to photoelectrically detect whether one or more papers of the same kind, have been placed in the same envelope by the machine. In this instance, the difference between the returned light level indicating the presence of the papers as compared to the absence of the papers is very small. As stated, in order to detect such a small change in the received light, the hysteresis of the photosensor needs to be low.
Alternatively, in high contrast sensing environments, it is preferably to have a photosensor with a large hysteresis so as to minimize the possibility of the photosensor""s producing an erroneous output due to noise. High contrast environments include, for example, the detection of the presence or absence of paper in a copier or a facsimile machine.
Based on the foregoing, it is clear that it is advantageous to be able to control the hysteresis of the photosensor such that it can be adjusted in accordance with the environment/application in which it will be utilized. However, currently, the hysteresis of many commercially available photosensors is preset by the manufacturer and cannot be altered by the purchaser. As such, the hysteresis of the commercially available photosensors cannot be optimized for operation in accordance with the intended application.
Accordingly, there exists a need for a simple, cost effective photoelectric sensing circuit that provides for the control of the hysteresis of commercially available photosensors. Specifically, the photoelectric sensing circuit must provide for adjustment of the hysteresis so that the photosensor can be optimized for operation in accordance with its intended application (i.e., low contrast or high contrast). Moreover, the circuit must be simple and inexpensive such that the use of the photoelectric sensing circuit is commercially feasible.
Accordingly, the present invention relates to a photoelectric sensing circuit that provides for variable control of the hysteresis of commercially available photoelectric sensors.
More specifically, the present invention relates to a photoelectric sensing circuit comprising a photosensor capable of receiving light and generating an output signal indicating the amount of light incident on the photosensor. The photosensor generates a first output signal when the level of received light is above a first predetermined level, and a second output signal when the level of received light is below a second predetermined level. The circuit further comprises a variable light source for generating and emitting the light incident on the photosensor and a power source coupled to the light source. The power source has a variable output level for controlling the intensity of the light emitted by the light source. Finally, the photoelectric sensing circuit also comprises a control circuit coupled to the variable power source for varying the output level of the power source. In accordance with the operation of the photoelectric sensing circuit of the present invention, if the photosensor is outputting the first output signal, the control circuit reduces the output level of the power source so that the intensity of the emitted light results in a level of received light which is below the first predetermined level, and if the photosensor is outputting the second output signal, the control circuit increases the output level of the power source so that the intensity of the emitted light results in a level of received light which is above the second predetermined level. The foregoing operation of the control circuit effectively changes the hysteresis of the photosensor, which as stated is preset by the manufacturer.
As described in detail below, the present invention provides important advantages over prior art devices. Most importantly, the present invention provides a simple, cost effective circuit that allows for variable control of the hysteresis of the photosensor. As such, the photoelectric sensing circuit of the present invention allows a given photosensor to be optimized for use in either a low contrast sensing environment or a high contrast sensing environment.
In addition, as the novel photoelectric sensing circuit is simple and utilizes currently available photosensors, the circuit represents a cost effective, commercially feasible solution to the problems associated with prior art photosensors.